Clean, viable blood has become a precious resource in this age of complex invasive surgeries for treatment of disease or injuries while donor blood supplies are becoming both scarcer and suspect in light of potential HIV and hepatitis contamination and transmission via transfusion. Autologous transfusion, the use of a patient's own blood drawn before elective surgery or from the surgical field during the procedure or postoperatively from the wound site, has been endorsed as the safest form of transfusion and has become increasingly more popular. Autologous transfusion is desirable because it eliminates the risks encountered with homologous transfusion of donor blood. The risks of homologous transfusion include disease transmission, transfusion reaction and decreased quality of bank blood stored over time.
Aside from eliminating risks of homologous transfusion, autologous transfusion is desirable because it acts as an immediate blood source for trauma cases, conserves blood bank blood for cases where autologous transfusion is inappropriate and provides an option for patients with religious convictions prohibiting use of donor blood. For trauma cases involving rapid bleeding, autotransfusion can prevent death by providing an immediate, large source of blood that doesn't need to be cross-matched. In cases of rapid, profuse bleeding, available banked blood may be depleted or the blood cannot be given fast enough.
Intraoperative autotransfusion is the recovery of the patient's blood lost during surgery and reinfusion of that blood at a later time during the procedure. The reinfusion can be direct or after processing of the blood performed in the operating room or a central facility. During bypass surgery, for example, blood returning to the right heart is removed by suction (referred to as cardiotomy) and returned to the blood circuit after processing to remove bubbles, debris and the like. In other procedures, the blood pooling at the operative site is removed by suction.
Postoperative autotransfusion is the salvaging of blood following surgery. Blood draining into the chest, for example, following surgery or trauma must be removed by a drainage or aspirating system to prevent its accumulation. Such blood is suited to salvage and reinfusion because it is usually defibrinated, sterile and does not need to be anticoagulated or washed prior to reinfusion.
FIG. 1 depicts in simplified form a system for collecting, without washing, and processing pooled blood at a patient's operative or postoperative surgical site 10 to reinfuse the blood in an autologous transfusion. Basically, blood is collected into a reservoir 12 (or directly into a reinfusion bag), through suction applied through surgical tubing 14 either by wall vacuum or by a roller pump, and filtered and reinfused. In one system as depicted in FIG. 1, blood is collected into a disposable liner bag 16 within a reusable rigid canister 18 forming the reservoir 12. The liner bag 16 has a filter 20, and the interior of the rigid canister 18 is connected to a wall vacuum source or roller pump through surgical tubing. Blood from the liner bag 16 is either drained by gravity into a transfer pack or is directly infused through an infusion catheter 22 (optionally using a roller pump) through the filter 21 back into the patient as depicted in the dotted line position of the liner bag 16 and filter 21.
Turning to the collection of the blood from the surgical site 10, the vacuum drawn through the surgical tubing causes suction to occur in the liner bag 16 to draw blood through flexible surgical tubing 26 extending to the attached suction tube or probe 30. Suction tubes or probes 30 come in many configurations, but basically are straight or curved, elongated tubular instruments having a fitting at one end for attachment to the surgical tubing 26 and an open tip end that may be submerged in the pooled blood at the site 10. A vacuum is drawn through the medical tubing 26 to suction the blood, debris and body fluids into the tip and convey it to the reservoir 12. Tip configurations vary, but efforts have been made incorporating end shields and/or side openings to inhibit closure of the opening on contact of the end with tissue and filters to filter out and inhibit obstruction of the openings by floating debris. Typically, the entire probe 30 is autoclavable for reuse, and the tips are removable for cleaning. Simple suction tubes are also referred to as aspirators and are used in other contexts to remove surgical debris during operative procedures or accumulated fluids and gases from closed surgical sites.
Anticoagulant from a container 24 is added either at the suction tip or is added to the collected blood before it is reinfused. In the example of FIG. 1, the anticoagulant is infused from anticoagulant container 24 through medical tubing 28 into the probe 30 and mixed with the blood being suctioned out in a manner suggested in U.S. Pat. No. 3,955,573, for example. The mixture may take place at the tip of or at the widened section near the attachment end with the tubing 26 and 28. Thorough mixing of the anticoagulant with the aspirated blood at the probe tip is advocated, and examples of tip configurations for effecting a vortex mixture of the blood and anticoagulant suctioned in by the vacuum drawn through the suction tube are depicted, in the '573 patent.
Infusing unwashed blood can mean infusion of high levels of free hemoglobin, debris from the surgical field and "procoagulants". The blood infused may also contain added anticoagulant as described above and irrigating solutions that may be used during the procedure to wash the surgical site 10. A wash fluid, e.g. a mixture of saline and anticoagulant, may also be introduced at the tip of the suction probe to wash the orifice and to add the anticoagulant as disclosed, for example, in U.S. Pat. No. 4,976,682, described below.
In a further U.S. Pat. No. 3,952,743, a probe used to remove tissue, e.g. brain tumor cells, has a coaxial tubular arrangement, and a wash fluid is introduced down and diverted in the outer tube to effect a vortex as it passes out of the outer tube at the tip to aid in removing any tissue caught at the orifice to the inner suction tube. The vacuum suction applied to the inner tube to suction the tissue also suctions the wash fluid directed to the probe tip. Thus, in different contexts, it is known to introduce a wash fluid with or without anticoagulant, to the tip of a suction probe or aspirator.
FIG. 2 depicts a system for washing the blood after it is collected which includes the additional apparatus and steps of adding and removing the wash fluid downstream from the probe 30, including the wash fluid container 40, reinfusion blood bag 42, reversible pump 44, centrifuge 46 and connecting surgical tubes 38, 48, 50, 52, 54. Valves 53, 55 and 57 are also included in tubes 38, 48, and 50, respectively to be opened or closed during these additional steps. The most widely studied and reported device for concentrating and washing red blood cells from salvaged blood is the Haemonetics Cell Saver system generally depicted in FIG. 2.
With the system of FIG. 2, blood is collected from the operating site using a double-lumen suction probe 30 which allows diluted anticoagulant to be mixed with blood as it is being aspirated. The mixed blood and anticoagulant solution (and any wash fluid in the operating site 10) is passed through a 180 micron macrofilter (not shown) to remove gross debris and is initially collected into a standard cardiotomy reservoir 12. When there is enough blood for processing, the mixed blood and anticoagulant solution is routed from the reservoir 12 into a centrifuge bowl 46 by opening valve 53 and operating reversible pump 44 in a first direction. Valve 53 is then closed and valve 55 is opened. In the centrifuge bowl, the blood is washed with an isotonic saline fluid, pumped from container 40 through the open valve 55, and concentrated. The supernatant layer containing white blood cells, platelets, plasma fractions, heparin, free hemoglobin, saline fluid and other cellular debris is generally discarded through the tubing 54. Then, the valve 55 is closed, and valve 57 is opened. The pump direction is reversed to pump the packed red blood cells into the infusion bag 42 and returned to the patient through tubing containing a 20 micron filter (not shown).
Many concerns exist or have existed regarding the reinfusion of salvaged blood (with or without the extra processing of FIG. 2), some real and some theoretical. The primary concerns are formation of microemboli and air emboli, disruption of normal coagulation, dissemination of infection or malignancy and hemolysis. Microemboli such as platelet aggregates can be removed by filtering blood through a 40 micron micropore filter prior to reinfusion to the patient. Concerns about air entrapment and resulting air emboli occurring during the processing and infusion of the blood have diminished with the incorporation of fail-safe air separation devices added to newer systems, and air embolization is unlikely with the new techniques and careful attention. Newer systems and the washing of salvaged blood have also nearly eliminated reports of coagulopathy. Dissemination of infection or malignancies have only infrequently been reported. The thrombocytopenia and minor coagulation disorders occurring after patients have had massive amounts of blood autotransfused are generally related to massive blood replacement and multiple injuries rather than to intraoperative autotransfusion per se.
Following salvage and processing, the number and proportion of cellular components are altered, some cells have decreased function and plasma components are missing, but red blood cell survival, resistance to lysis and function is normal. White cell counts range from 6600 to 17000 per microliter and the cells are severely damaged. Mean platelet counts have been found to be 16000 to 67000 per microliter, and the platelets are likely to have decreased function or no function because of mechanical damage during filtering and suctioning. Potassium levels are low (1.5 mmol/l), proteins are lost, and the product is devoid of coagulation factors. The washing also removes undesirable parts of the unwashed blood such as free hemoglobin and myoglobin from the plasma as well as cellular debris, particles of bone, activated clotting factors and activated platelets. Intact red blood cells following salvage, centrifuging and washing have normal survival, resistance to osmotic lysis and function. The red blood cells have normal to increased levels of 2,3 DPG but are potassium depleted. Typical hematocrit levels are 50-60%.
Hemolysis is a genuine concern. The suctioning of blood that occurs with autologous transfusion has been found to be harmful to the blood, particularly to platelets, red blood cells and elements of the immune system. This damage is believed to be caused by the suction of air bubbles with the blood components which causes hemolysis, clot formation or "drying" of the blood as noted in the above-referenced '682 patent and elsewhere. The high level of free hemoglobin encountered with vacuum suctioning of blood (and not removed by centrifuge) has been associated with acute cases of renal dysfunction and failure. Excessive vacuum levels leads to blood cell damage due to turbulent sheer stress and causes suctioning of air mixed with the blood and is a major cause of hemolysis as the air bubbles mix with and contact blood cells. The resulting red blood cell damage also diminishes the amount of packed red blood cells that can be recovered and returned to the patient during autologous transfusion.
Cardiotomy suction is indicated as a primary factor in the hemolysis that occurs with cardiopulmonary bypass operations. It has been reported that during a half-hour of perfusion, hemolysis was not detected, but at the initiation of intracardiac suction, hemolysis started to rise and showed a steady increase in plasma hemoglobin with continuous suctioning. The hemolysis in the general circuit remained low until the suctioned blood was added to the circuit. Other studies showed that plasma hemoglobin levels jumped and increased rapidly with the start of cardiotomy suction. Following cardiopulmonary bypass in human patients, plasma hemoglobin in the radial artery averaged 41 mg/dl but in the cardiotomy reservoir blood averaged 384 mg/dl.
The above-referenced '682 patent discloses a recognition of these problems and attempts to reduce the contact of air bubbles with blood, and the resulting hemolysis, during suction. The probe is provided that attempts to avoid the suction of air by supplying an anticoagulated wash fluid forming a "dynamic droplet" at the probe tip inside a porous shield. As a vacuum is applied, blood passing through the porous shield and the wash fluid are drawn in by suction, purportedly minimizing the suction of air, should the site become dry of blood. A system is provided, including an air bubble detector in the suction probe, for regulating the suction in proportion to the bleeding rate at the wound site and the quantity of bubbles detected in the solution passing through the probe. As bubbles are detected, the suction rate is increased or decreased in an effort to reduce the bubble concentration.